APRIL. 85 



discover anything stirring. Yonder are two black Water 

 Beetles (Colymbetes) ; see how they hurry to the top of the 

 water, then scuttle down again to the bottom, and hide un- 

 der the mud. 



C. I have one of them. 



F. This insect is worth a moment's observation. Ob- 

 serve how smooth its surface is, without any projections, 

 to adapt it for swift progress through so dense a medium as 

 water : the elytra shut very closely, to prevent the wings 

 beneath, which are large and long, from becoming wet and 

 unfit for use : the fore and middle feet are small and weak, 

 but the hindmost pair are very large and strong, and thickly 

 fringed with hair ; they are used as oars to propel the insect 

 through the water, and we may see how admirably they 

 are fitted for this purpose, by observing the effect produced ; 

 for the motion of the aquatic beetles is very swift. There 

 are many species of the tribe, but all agree in these particu- 

 lars : some are of very large size ; this is but a small kind. 



C. Here are some larvae of the Ephemera. They keep 

 the fin-like appendages at their sides constantly in a waving 

 motion, even when they themselves are at rest : what can 

 be the reason ? 



F. I believe these fins are connected with the air-pipes, 

 and are in fact breathing organs : and as they extract the 

 oxygen from that portion of the water with which they are 

 immediately in contact, I suppose their constant vibration is 

 necessary to produce a current, and so bring fresh particles of 

 water to be inhaled. But I apprehend these likewise perform 

 a double office, and are also organs of locomotion. 



C. There is a serpentine motion of the abdomen when 

 they swim, which perhaps aids them in some degree ; but 

 they do not appear to swim with the same facility as most 

 water-insects. I see some of these are in the pupa state, by 



